(i) Field of the Invention
The present invention relates to a rack and pinion steering device which converts the rotary motion of a steering wheel into a linear motion for turning, via tie rods, a set of wheels.
(ii) Description of the Related Art
In a conventional rack and pinion steering device, as shown in FIG. 3, a rack shaft 100 is slidably supported by a device unit 102, and a piston 104, attached to one end of the rack shaft 100, is slidably inserted into a cylinder tube 106. By the rotation of a steering wheel (not shown), an input shaft 108 is rotated, causing the rotary motion to be converted into the linear motion of the rack shaft 100 by a rack and pinion mechanism 110. This conversion to the linear motion of the rack shaft 100 is assisted by a hydraulic pressure being applied to the piston 104 in accordance with the rotating direction of the steering wheel.
Further provided is a slit 112, formed along an axial length of the device unit 102, and a key member 114, which is attached to the rack shaft 100 and is slidably engaged in the slit 112. Attached to the key member 114, via ball joints 120 and 122, are opposite tie rods 116 and 118. Additionally, bellows 124 are provided around the device unit 102 to cover the slit 112.
In order to allow the key member 114 to slide in the slit 112, a moderate clearance is necessary between the key member 114 and the inner wall of the slit 112. Furthermore, a moderate clearance is also required for the engagement between a rack and a pinion (not shown) in the rack and pinion mechanism 100.
However, in the above mentioned conventional device, a counter-rotary moment is exerted on the rack shaft 100, via the opposite tie rods 116 and 118, by the kickback of the wheels, and the reaction of the steering wheel at the time of operation. As such, this counter-rotary moment is received by the key member 114 engaged in the slit 112. Thus, a problem is caused because the counter-rotary moment received by the key member 114 results in the generation of unusual sounds and vibrations, in some cases, due to the necessary clearance required in the rack and pinion mechanism.